It happened at the Virginia Tech shootings in 2007, a commuter train crash in Los Angeles the next year, the movie theater massacre in Aurora, Colorado, last July and, again, at the night club fire in Brazil that killed 231 people on Sunday.

The incessantly ringing phones, and the realization that someone is desperately trying to reach someone else who is now dead, short-circuits the psychological defenses first responders need to do their jobs, said Jim Crabtree, a registered nurse who helps train them for the Los Angeles County Emergency Management Services Agency.

Hundreds dead in Brazil nightclub fire – Relatives and friends of Paraguayan student Guido Britez, 21, who died in a fire at the Kiss nightclub in Brazil, carry his coffin during the funeral in Asuncion on Tuesday, January 29. More than 230 people died and more than 120 were injured early Sunday when a fire tore through the nightclub packed with university students in southern Brazil, police said.

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Hundreds dead in Brazil nightclub fire – Guido Britez's family attends the funeral on January 29.

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Hundreds dead in Brazil nightclub fire – Mauro Hoffman, co-owner of the Kiss nightclub, is taken into custody by police in Santa Maria, Brazil, on Monday, January 28.

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Hundreds dead in Brazil nightclub fire – Residents of Santa Maria, Brazil, hold a march on January 28 to honor the victims of the Kiss nightclub fire and demand justice for them.

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Hundreds dead in Brazil nightclub fire – Residents march along Rio Branco Avenue on January 28, demanding justice for and to honor the Kiss nightclub fire victims.

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Hundreds dead in Brazil nightclub fire – A violinist comforts another during the march on January 28.

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Hundreds dead in Brazil nightclub fire – Demonstrators carry candles through the streets in Santa Maria on January 28.

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Hundreds dead in Brazil nightclub fire – Soldiers carry the coffin of a victim of the nightclub blaze on January 28.

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Hundreds dead in Brazil nightclub fire – A priest celebrates Mass in a public square in the center of Santa Maria on January 28.

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Hundreds dead in Brazil nightclub fire – Mourners cry at the municipal cemetery on January 28.

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Hundreds dead in Brazil nightclub fire – The entrance to the Kiss nightclub is covered in soot on January 28.

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Hundreds dead in Brazil nightclub fire – Relatives and friends of one of the victims of the Kiss nightclub fire gather during the funeral at Santa Rita Cemetery in Santa Maria on January 28.

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Hundreds dead in Brazil nightclub fire – Firefighters stand at the burnt-out entrance of the Kiss nightclub on Sunday, January 27, in Santa Maria, Brazil.

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Hundreds dead in Brazil nightclub fire – Relatives wait to identify victims at the municipal gymnasium in Santa Maria on January 27.

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Hundreds dead in Brazil nightclub fire – Relatives of victims weep during a funeral in Santa Maria on January 27.

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Hundreds dead in Brazil nightclub fire – Relatives pray at the wake of a victim on January 27 in Santa Maria.

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Hundreds dead in Brazil nightclub fire – Relatives of a victim of a fire that broke out at the Kiss nightclub weep during the funeral in Santa Maria, Brazil, on Sunday, January 27.

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Hundreds dead in Brazil nightclub fire – A woman weeps on a coffin as relatives of the nightclub fire victims identify bodies.

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Hundreds dead in Brazil nightclub fire – People console each other during a collective wake for the victims of the nightclub fire.

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Hundreds dead in Brazil nightclub fire – A coffin decorated with a photograph and image of the Virgin Mary is surrounded by mourners.

Hundreds dead in Brazil nightclub fire – Emergency personnel gather outside the burned-out Kiss nightclub in Santa Maria, Brazil. The nightclub is popular with young people, drawing between 2,000 and 3,000 people a night on the weekends.

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"It starts ringing and it becomes an instant reminder that this person is human, that they have friends and family who care," he said.

It also leaves responders with an uneasy feeling they're keeping a secret from the victim's loved ones, Crabtree said.

Crabtree first ran across the issue following the Virginia Tech shooting, in which a lone gunman, a student, killed 32 people.

Some first responders couldn't get the sound of ringing cell phones out of their ears, psychologists Christopher Flynn of Virginia Tech and Dennis Heitzmann of Penn State wrote in a follow up journal article.

"As police and rescue workers removed the bodies of the deceased and evacuated the survivors, they reported haunting memories of cell phones ringing in body bags as parents and friends desperately called their loved ones."

Los Angeles first responders dealt with the same issue when a commuter train collided with a freight train in 2008.

Hundreds of firefighters and other first responders flooded the scene, clawing through the mangled wreckage to get at the bodies of victims. All the while, Crabtree said, dozens of cell phones kept ringing.

Aurora police Officer Justin Grizzle spoke this month during a court hearing of entering a theater where 12 people died in that shooting rampage.

It was the same Sunday night, when firefighters rushed through a hole punched into the wall of the Kiss nightclub by people who had escaped the building after it caught on fire.

They found dozens of bodies of club-goers who died of smoke inhalation. And they once again heard the sounds of ringing phones.

Milton Neves, a reporter from Radio Bandeirantes, said some 800 to 900 mobile phones were going off at the same time. One alone had 104 missed calls.

Hundreds of family and friends were desperately trying to reach loved ones who were at the nightclub in the Brazilian city of Santa Maria when a fire swept through early Sunday, killing at least 230 people and injuring hundreds more.

"It was a really complicated scene. A lot of smoke, a lot of shoes that were left, cell phones, because everybody tried to get out of there running," Glauber Fernandes, a reporter for CNN affiliate Band News said.

"While we were there, we saw the cell phones were ringing. It was parents, friends, trying to know about what was happening and nobody was answering."

Few, if any, agencies have policies on what to do about the multitude of ringing phones police and firefighters frequently encounter at disaster scenes, Crabtree said.

He said he tells trainees turning off the phones can help save their own sanity, but says some agencies could view the act as tampering with evidence.

He favors policies that would allow responders to turn the phones off, but says most commanders haven't yet come to the same conclusion.

"It's a 21st century problem," he said.

But it's an issue emergency agencies will have to deal with sooner or later, if the experience of first responders Crabtree has spoken to is any indication.

"They don't talk about it openly, but when you get them alone ... " Crabtree said, like the responders, leaving the rest unspoken.